An inkjet printer is conventionally used, and in the inkjet printer, while a head part having a plurality of outlets is moved relative to an object, ejection of fine droplets of ink from each outlet is controlled to record an image. In the inkjet printer, for example, an ejection pulse is inputted to a piezoelectric element provided in the vicinity of each outlet in the head part to eject a droplet(s). In Japanese Patent Application Laid-Open No. 8-336970, disclosed is a technique where a plurality of ink droplets which are sequentially ejected at a constant frequency are merged during their flight to form a dot, since a driving signal is determined in consideration of Helmholtz frequency of a pressure generation chamber in a recording head. In Japanese Patent Application Laid-Open No. 2002-113860, disclosed is a technique where a landing position of a satellite ink droplet associated with a main ink droplet is aligned to a landing position of the main ink droplet, since a waveform of microdot driving pulse (ejection pulse) is set such that a flight speed of the satellite ink droplet is higher than a flight speed of the main ink droplet.
In the case where a plurality of droplets are merged during their flight or a landing position of satellite droplet is aligned to a landing position of main droplet, since a plurality of dots each having an almost circular shape are arranged regularly, there may be a case where an edge of an area represented by a group of dots becomes jagged (convexo-concave) or a density of an area to be represented by the maximum gray level (i.e., the area is a solid area of ink) becomes lower due to existence of gaps between dots. It is thought to suppress lowering of the density in the solid area by enlarging each dot by increasing an amount of ink included in a droplet. However, an outer edge of the area is swollen in this case.